1. Field of the Invention
This invention relates to an image recording apparatus for recording images on a recording sheet, such as an electronic typewriter, a facsimile apparatus or a thermal printer. The present invention also relates to an image recording apparatus capable of automatically selecting one-direction recording or both-direction recording by detecting the presence of an ink ribbon, and efficiently accomplishing recording without any wrong operation.
2. Description of the Prior Art
Description will hereinafter be made with a so-called serial type thermal printer taken as an example of the image recording apparatus.
FIG. 1 of the accompanying drawings shows a serial type thermal printer according to the prior art. A thermal head 3 attached to a heat sink 2 is mounted on a carriage 1 and is slidable along a guide shaft 4. Also, a ribbon cassette 6 containing an ink ribbon 5 therein is removably placed on the carriage 1. The ink ribbon 5 is supplied from a supply roll 5a provided in the cassette 6 to between a recording sheet 8 on a platen 7 and the thermal head 3 and thereafter is taken up by a take-up roll 5b, and the ink on the ink ribbon 5 is transferred to the recording sheet by the heat of the thermal head 3 corresponding to image information. Designated by a, b, c and d are guide pins. An Electric power for heating is supplied from a connector 10 on a printing base plate 9, fixed to the chassis of the printer, to the thermal head 3 through a flexible cable 11.
Further, in this thermal printer, heat-sensitive recording becomes possible by removing the ribbon cassette and replacing the recording sheet with heat-sensitive recording paper and thus, the thermal printer can be used as an apparatus for both heat transfer recording and heat-sensitive recording.
Now, generally, the relation between the recording sheet and the ink ribbon when heat transfer recording is effected with the ribbon cassette mounted so that a relative velocity is not created between the two. This is in order that the recording sheet and the ink ribbon are rubbed against each other to stain the recording sheet.
FIG. 2a shows a case where the ribbon take-up direction 12 and the carriage movement direction 13 are opposite to each other, and in this case, the carriage movement velocity V.sub.2 and the ribbon take-up velocity V.sub.1 are in the relation that V.sub.1 =V.sub.2 and the relative velocity between the recording sheet 8 and the ink ribbon 5 is zero. On the other hand, FIG. 2b shows a case where the ribbon take-up direction 12 and the carriage movement direction 14 are identical to each other, and in this case, the sum V.sub.1 +V.sub.2 of the carriage movement velocity V.sub.2 and the ribbon take-up velocity V.sub.1 is the relative velocity between the recording sheet 8 and the ink ribbon 5, and relative movement is inevitably created between the two. So, in this case, the ink ribbon can be fed in the opposite direction, but if this is done, the used ribbon which has lost ink is fed to the front of the thermal head and thus, recording becomes impossible. For the reason as set forth above, when heat transfer recording is to be effected in the conventional thermal printer, only one-direction recording can be accomplished and accordingly, the thermal head on the carriage has been urged against the recording sheet during the forward movement thereof to effect recording on the recording sheet, but has been spaced apart from the recording sheet during the backward movement thereof. However, with such a construction, only one-direction recording can be accomplished even when heat-sensitive recording is to be effected and thus, the recording speed decreases by half.